So I recently got MCP working on my Mac and I can edit code and it works fine. But I have to restart the whole game to start the new edited code, I've seen people on youtube videos that can just stream their code to Minecraft without restarting the game. Just not sure how to do this.
Are you using an IDE to edit your code in, such as Eclipse or IntelliJ? There are usually two options for starting your game in those environments, a "run" option and a "debug" option. If you use debug mode, the IDE can dynamically update your code running in Minecraft without having to restart the game. You will still have to restart the game when you change method signatures or perform large code changes when the game is running, but you'll have to do so a lot less often than if you didn't use debug mode.